The present invention relates to heat resistant cast iron-nickel-chromium alloy, and more particularly to heat resistant cast iron-nickel-chromium alloy which essentially has the composition of austenitic cast alloy containing Cr, Ni, Nb and W and which is excellent in creep fracture strength at high temperatures and in resistance to thermal impact or carburizing.
HK 40 which is a heat resistant cast alloy containing Ni and Cr (25 Cr-20 Ni steel, see ASTM A 608) and HP materials (see ASTM A 297) have been used as materials for ethylene cracking tubes in the petrochemical industries. With the elevation of operating temperatures in recent years, it has been required to improve the high-temperature characteristics of such materials. To meet this requirement, HP materials containing Nb and W or HP materials containing Nb, W and Mo have been developed and placed into use. However, with the recent tendency toward severer operating conditions, it is desired to provide materials which are superior to such HP materials containing Nb and W, or Nb, W and Mo in respect of high-temperature creep fracture strength and resistance to thermal shock or carburizing.